Experimental study on sand production and seabottom subsidence of non-diagenetic hydrate reservoirs in depressurization production

Nature gas hydrate mainly exists in non-diagenetic strata, and sand production and reservoir subsidence often happen during mining, which restrict the safe and sustainable production of gas hydrate. In order to study the relationship of sand production and reservoir subsidence with temperature, pressure, gas production, water production of hydrate exploitation, simulation tests under different conditions were conducted with a self-developed device for sand production and sand control. It is observed that the sand ratio and grain size of water gradually increased in the first two production stages; For fine-grained sand reservoir, increasing the gas production rates will enhance the sand carrying ability of water, so that the sand production risk increases. At the same time, high-gas-production will accelerate the temperature decrease and lead to the formation of ice-phase, and/or ice blocking. The reservoir subsidence during hydrate exploitation is closely related to hydrate content in the reservoir. However, the influence of gas production rates and depressurization rates on reservoir subsidence are related to gas production mode. The stimulation operation in the mid-late stages of hydrate exploitation will increase sand production risk and subsidence. We further discussed the sand production taking the first marine hydrate mining case in Japan in 2013 and proposed the concept of sand prevention according to grades and stages.